The future of architecture is lightweight, streamlined, and sleek as a cat on a hot photovoltaic roof. But sometimes, you can't help looking at these futuristic architectural designs, full of space-age supports and gravity-defying structures, and think, "No way would I ever actually go up to the top of that thing."

Here are the 10 most terrifying futuristic architectural projects, in no particular order. Some of these are already being built, others are just conceptual at this point. They're all utterly beautiful, daring and clever solutions to the architectural and environmental challenges of the 21st century. But they're also utterly terrifying to architectural laypeople like ourselves.

10) Above is the Taichung Tower project, designed by DSBA and expected to open this year. The 300-meter-tall tower features "floating observatories" made of lightweight materials from the aerospace industry, which can move up and down the "trunk" and hold up to 80 people each. And they're held up by helium, and an electromagnetic field! Would you ever dare to go up in one of those "observatories"? More details at Inhabitat.

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9) "The Cloud" is a design for a resort city in Dubai, which would "float" 300 meters above the ground, on slanting see-through legs that are meant to look like rain. It's designed by Nadim Karam of Lebanese architect Atelier Hapsitus. [via DesignBoom]

8) The Aeromodeller II by Lieven Standaert. The phrase "sustainable zeppelin" should be enough to strike fear into anyone's heart. According to GreenMuze, the Aeromodeller "has the ability to invert its propellers that then double as windturbines to generate electrical energy to electrolyse captured rainwater into hydrogen and oxygen. The hydrogen is used to keep the ship airborne and used in fuel cells to power the ship."

7) The Tokyo Mega-Pyramid One of the hallmarks of awesome futuristic architecture, of course, is the arcology — the idea of a megastructure that can hold a whole city's population in one self-sufficient building. It's only when you combine that idea with the passion for light-weight building materials that things get scary.

Case in point: this floating mega-pyramid would house 750,000 people inside more than 50 pyramid structures suspended in the main pyramid. And you'd travel around the mega-pyramid via Personal Rapid Transit Pods. The whole shebang would be powered by a photovoltaic coating on its surface, or possibly algae. Alas, the space-age lightweight materials needed to build this wonder still don't quite exist. [via Travel and Leisure]

6) The New Orleans Arcology Habitat (NOAH). Here's another proposed future floating arcology, this time on the banks of the Mississippi. This structure would house 40,000 people and utilize a multi-cavity "hull" as the foundation for the superstructure. As Yanko Design explains:

Noah, at its current height of 1,200 feet will rest up its triangulated foundation constituted to be a buoyant multi-cavity "hull." This "hull" will consist of high strength concrete cells, forming approximately a 40×40 matrix. This matrix not only gives buoyancy to the structure, it also becomes the framing matrix for the steel framed superstructure. It is estimated that the combined weight of NOAH will draft 180 feet within the water-filled basin, allowing a minimum 50 foot space between the floor of the basin and the floor of the buoyant foundation.,

True, a pyramid is one of the most stable shapes there is. But of course, as they note, New Orleans has been known to experience some extreme weather events, and you wouldn't necessarily want to be at the apex of that pyramid during one of those. Yanko also has info about a floating arcology project for Boston, the BOA.

5) The Floating Aerohotel. We wrote about this one a while back. It combines some of the scariest things on Earth: You can only reach it via zeppelin. And its minimal support systems create the impression that it's so light and airy, it would float away if not tethered down. Plus it's over the ocean.

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4) The Water-Scraper. Designed by Malaysian architect Sarly Adre bin Sarkum, this tower would be almost as tall as the Empire State Building — but only the top two stories would be above the water level. The building would generate its own power using wave-power, solar energy and wind power, and has its own farms, including aquaculture and hydroponics farms. And it's kept upright "using a system of ballasts aided by a set of squid-like tentacles that generate kinetic energy." It's a long way down to the bottom of the ocean. [via Morsfis]

3) Tower City. This entrant in the 2010 eVolo Skyscraper Competition imagines the whole city of Marseilles being replaced with a "stacked skyscraper" that rests on stilts. Stilts! And they're built of "recycled building materials" from the old city. It's an ecotopia, and it looks as lovely as all get out — but would you feel safe standing on a skyscraper stacked on top of other buildings, which in turn was on stilts — built out of recycled material? As the architects explain:

This project consists of a pragmatically and ambitious system which is compact and complete, thus enabling to obtain a new density. The city will no longer be, as it is today, a set of elements organized in a single plan but rather a set of modules laid out in a 3D structure. The city as it is today is simply positioned vertically and sustained by horizontal plans. And the life which starts organizing there allows, horizontally and vertically, to carry out the usual functions of a city : living, working, travelling, consuming, entertaining etc.

2) Inverted Cube Houses These actually exist, and they're part of a hair-raising gallery of "gravity-defying homes" over at Elle Decor. As Elle Decor explains: "Architect Piet Blom tipped a conventional house forty-five degrees and rested it upon a hexagon-shaped pole so that three sides face down and the other three face the sky." It's cool and futuristic-looking, but also alarming. Other scary items in Elle Decor's gallery: the German rotating building and the building that extends out over a canyon in Australia, with no apparent support.

The orientation was developed to maximize the use of solar energy. Strong decisions and consequence in driving its proportions guarantee the uniqueness of (formo)design. Dynamic and simple form are the result of the yach architecture interpretation. The core, made of concrete, is combined with steel cantilever structures. Foundation for the house is a concrete counterweight foot stabilizet with the sea bed pile system.The floating deck, which rises with the water level thanks to the railing installed in the core structure, leads you to the stairway. The top deck is available for the residents as well.

Plus the thing can only be reached via water, so you'd better hope there's a boat nearby.